OSU Bighorn sheep research sheds light on killer disease

CORVALLIS, Ore. - With their ability to climb steep rocky mountain areas, California bighorn sheep live in some of the most rugged environments Oregon has to offer.

No matter how high they go, the wild sheep can’t elude Mycoplasma ovipneumoniae – the bacteria now widely thought to be primarily responsible for fatal infectious pneumonia in bighorns.

Respiratory disease has killed numerous wild sheep in Oregon and other Western states over the past few decades and is considered the largest risk to wild sheep populations, according to the Oregon Department of Fish and Wildlife.

Once a herd is infected, an all-age die-off can occur, and the disease remains chronic in the population.

Now, Oregon State University researchers are studying several aspects of the California bighorn sheep herd in the state – including movement, habitat use and survival – to gain insight into the animal’s risk for contracting the killer strain known as M. ovi (pronounced m-ovee). The disease spreads through contact between domestic sheep flocks and bighorn sheep, or from bighorn to bighorn.

Oregon is home to about 3,700 California bighorn sheep in 32 different herds in Central and Southeast Oregon.

ODFW traditionally captures and relocates California bighorn sheep around the state each year to improve genetic diversity and restore this rare species to its historic range in Oregon. But these relocation efforts are on hold this year while wildlife managers learn more about M. ovi, partly through the work being done at OSU.

Often, the first contact with a particular strain of pneumonia kills bighorn of all ages, according to OSU wildlife biologist Clint Epps. Some adults survive, but then as the infection persists their lambs die every year. A bighorn herd might not recover for decades.

Wildlife managers strive to keep wild and domestic sheep and goats separate to avoid transmission of the disease.

“There is a high-stakes need to understand where the pathogen is likely to enter a bighorn population and where it’s likely move after that,” Epps said. “In the past few years, wildlife agencies in the West have made decisions to remove certain individual animals, or all individuals in the herd, to prevent the spread of disease.”

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